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I'm new at SFG. I decided to tack landscape fabric and hardware cloth to the bottoms of my boxes. Now I'm procrastinating because I'm worried that if I lay the boxes on a length of landscape fabric to keep weeds from coming up between boxes, they might not get enough drainage having 2 layers of cloth underneath.

I don't think two layers will cause any drainage problem at all. It will be in contact with the ground so even if it is a very tight weave then the water will soak out - think of a canvas tent in a rainstorm, as soon as you touch the canvas the water soaks in. I believe the weeed barrier will behave the same.

You can put two layers in a sieve and fill it with water. Then you can see if it will drain as you hope.

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I have seen women looking at jewelry ads with a misty eye and one hand resting on the heart, and I only know what they're feeling because that's how I read the seed catalogs in January - Barbara Kingsolver - Animal, Vegetable, Miracle